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Originally Posted by gnormhurst
Okay, let me play devil's advocate.
Wheel encoders have been done before, and I assume they work. If a robot uses differential (two-wheel) drive and we keep track of each wheel's motion, and the tires are pneumatic and don't ever slip on the carpet, can't we measure not only x and y but rotation as well?
So my question is this: what great advantage does an optical mouse have over wheel encoders that makes us want to make this work? Other than being really cool, that is.
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The problem is that wheel slippage always occurs, in every turn one makes (not to mention once pushing becomes a factor). Some robots with conventional swerve-style steering have a differential to minimize (but not by any means eliminate) this, but therein lies the problem. An encoder or hall effect sensor is placed somewhere on the drivetrain, which propels the robot, but does not reflect its actual movement as accurately as some would like. You are absolutely right that this usually doesn't prove troublesome to robots that steer as you describe, but they represent a minority in FIRST. This problem is especially the case with tank-style steering robots, i.e. most robots.
Enter terrain-following. Instead of looking at what the propulsion device is doing to estimate where the robot is, we are following the movement of the robot. Assuming the camera doesn't skip a beat and screw up, we get a much more accurate guidance system that opens up possibilities of pinpoint accuracy.